A great deal of development research is currently under way on renewable energy and clean energy with increasing concern about depletion of fossil fuels and environmental pollution. It has been widely studied in the field of thermoelectric conversion which allows direct generation of electricity from a solid state, eliminates noises and shakes, and generates thus electrical energy only with temperature difference.
A thermoelectric conversion was first developed by Seebeck, a German physicist, in 1821 by discovering the creation of electromotive force when each of two different metals joined in two places was exposed to a different temperature. Conventional thermoelectric devices developed in US and Japan use p-n junction and most of developments were focused on thin films of high efficient thermoelectric materials. Most of thermoelectric materials having properties of a metal compound show thermoelectric conversion by a temperature difference between two electrodes (ΔT between + pole and − pole). Thermoelectric efficiency depends on the figures of merit ZT as shown below.
  ZT  =                              α          2                ⁢        σ        ⁢                                  ⁢        T            k        ⁢          {                                                                  α                ⁢                                                                  ⁢                Seebeck                ⁢                                                                  ⁢                coefficient                            ⁢                                                                                                                                      σ                ⁢                                                                  ⁢                electrical                ⁢                                                                  ⁢                conductivity                            ⁢                                                                                                                                      κ                ⁢                                                                  ⁢                thermal                ⁢                                                                  ⁢                conductivity                            ⁢                                                                                                                      T              ⁢                                                          ⁢              average              ⁢                                                          ⁢              absolute              ⁢                                                          ⁢              temperature                                          
However, such a thermoelectric material reacting by a temperature difference between two electrodes has very low thermoelectric efficiency compared to its weight and size and thus, it is not possible to use as an energy source. Further, a thermoelectric material reacting at a high temperature difference (ΔT=150-700° C.) has disadvantage of requiring a large waste heat recovery system such as incinerator.
A metal ammonia and metal amine material used as a solvating material has been confirmed only for its possibility that can be utilized as a new energy source. It is still in the experimental state for its electrical phenomenon. Since only articles have been reported so far that a solvating material shows thermoelectric effect at 65° C. below zero to 35° C. below zero, it is still in a basic development stage.
A solvating material which is a compound including solvated electrons has both metallic properties and non-metallic properties depending on a metal concentration. M(NH3)n as a solvating material, which is prepared by reacting with an alkali metal or alkali earth metal, lanthanum metal or actinium metal, etc. at 34° C. or less below zero where it exists in a liquid state, is separated into M(NH3)n-x and xNH3. Alkali metals, alkali earth metals, lanthanum metals and actinium metals, which correspond to M, have high reactivity to be easily oxidized when they are exposed to water or oxygen, while NH3 lowers reactivity since its gas is light and scattered into the air easily. M(NH3)4, in which n is 4, is relatively stable. Equation to synthesize a solvating material is as follows.Li(s)+xNH3(fluid)→Li(NH3)(l)
A solvating material existing in a liquid state is bronze color with higher saturated concentration in ammonia, which is one of usable solvents, and also has physical properties similar to a metal having metal ions and free electrons, and high electrical conductivity. When a concentration of metal ammonia is 0.01 MPM or less, it has electrolyte characteristics including solvated electrons and solvated cations, when it is 2-5 MPM, its characteristics change from non-metal to metal, when it is 4 MPM, free electrons are generated, when it is about 20 MPM, it has electrical conductivity similar to mercury, and when it is 22 MPM, it has 15000 Ω−1 cm−1 of electrical conductivity which is higher than that of mercury (10000 Ω−1 cm−1).
Color of the solvating material is determined at various concentrations. When the concentration is 22 MPM at which it shows metallic characteristics, it becomes bronze. The color gradually becomes lighter with lowered concentration changing from red to blue which is shown at a concentration of 2 MPM. The reason to show a blue color at a low MPM is that the ammonia surrounds electrons (called as solvated electrons). One electron is released from a metal by an ionization reaction in a metal solution as suggested by Kraus, Mmetal→Ms++es−, and surrounded by NH3. In case of lithium, when lithium is dissolved in an ammonia solution, an electron is released from lithium which is then turned to lithium ion (Li+) as shown below.Limetal→Lis++es−
Alkali metals, alkali earth metals, lanthanum metals and actinium metals, which have generally high electron density, release an electron while dissolved in an ammonia solution and is surrounded by ammonia, which forms then solvated electrons. An electrochemical oxidation reaction of a solvating material solution when M is lithium is as follows.Li(NH3)X(l)→Li++xNH3(g)+e−
The solvating material solution is decomposed to a free electron and ammonia gas. The generated electron and ammonia are combined to form solvated electrons at a low concentration and the electron is released to a free electron at a high concentration.
es−(iNH3), which is in a solvated electron state, generates a free electron, ef−, with increasing concentration of the solvated metal, while when NH3 is added or a concentration of the material is lowered, the solvated electron, es−(iNH3), is generated as shown below.es−(iNH3)ef−+NH3 
A solvated electron founded at a concentration of 8 MPM or less is a combined form of the electron released from a metal and ammonia molecule. The combined forms between electrons and ammonia molecules increase and it becomes an insulator when the concentration gets lowered, while electrons are released from the solvated electrons when the concentration gets higher. It is noted that when the concentration is 4 MPM or higher, free electrons are found.
As described above, solvated electrons, which are combined forms of electrons generated from the metal and ammonia, are generated according to synthetic concentration of a solvating material. Even though thermoelectric performance is noted from the oxidation reaction with temperature changes and electron releasing and combining phenomenon of solvated electrons with metal concentration changes, alkali metals and alkali earth metals, lanthanum metals and actinium metals have high reactivity to be oxidized easily when they are exposed to water or oxygen and NH3 lowers reactivity since its gas is light and scattered into the air easily. Therefore, there is demand on developing a thermoelectric conversion device which can maintain a solvating material in a reversible condition in the mechanism of separating into free electrons and solvent gas from a material including solvated electrons by heat, increasing internal pressure by the gas generated from the separated material, and generating electrical energy by releasing electrons.